Bottom Line:
In this approach, Fe(NO3)3 · 9H2O is used as the iron source, and polyvinylpyrrolidone (PVP) acts as a surfactant in the presence of NaCl in mixed solvents of H2O and ethanol.One of the advantages of this method is that the size of α-Fe2O3 mesoporous microspheres can be adjusted in the range from ca. 170 to ca. 260 nm by changing the experimental parameters.High photocatalytic activities in the degradation of salicylic acid are observed for α-Fe2O3 mesoporous microspheres with different specific surface areas.

ABSTRACTA simple one-step NaCl-assisted microwave-solvothermal method has been developed for the preparation of monodisperse α-Fe2O3 mesoporous microspheres. In this approach, Fe(NO3)3 · 9H2O is used as the iron source, and polyvinylpyrrolidone (PVP) acts as a surfactant in the presence of NaCl in mixed solvents of H2O and ethanol. Under the present experimental conditions, monodisperse α-Fe2O3 mesoporous microspheres can form via oriented attachment of α-Fe2O3 nanocrystals. One of the advantages of this method is that the size of α-Fe2O3 mesoporous microspheres can be adjusted in the range from ca. 170 to ca. 260 nm by changing the experimental parameters. High photocatalytic activities in the degradation of salicylic acid are observed for α-Fe2O3 mesoporous microspheres with different specific surface areas.

Mentions:
We have measured the BET-specific surface areas and the pore size distributions of samples 1 and 6. Figure 5a, b shows the nitrogen adsorption–desorption isotherms and the pore size distributions of samples 1 and 6, which indicate that the BJH (Barrett–Joyner–Halenda) desorption average pore size and the BET-specific surface area are 4.3 nm and 114 m2/g for sample 1, and 7.9 nm and 37 m2/g for sample 6, respectively. Figure 5 indicates that there exist mesoporous structures in the α-Fe2O3 mesoporous microspheres. Sample 1 prepared at a lower temperature (120°C) has a much higher specific surface area and narrower pore size distribution than those of sample 6 prepared at a higher temperature (140°C). From the comparison of TEM micrographs of samples 1 and 6 (Figures 2, 4), one can see that the nanocrystals self-assembled in α-Fe2O3 mesoporous microspheres of sample 1 are smaller than those of sample 6. The oriented organization of smaller nanocrystals in α-Fe2O3 microspheres of sample 1 leads to smaller average pore size (4.3 nm); in contrast, the bigger nanocrystals in α-Fe2O3 microspheres of sample 6 result in larger average pore size (7.9 nm). On the other hand, the mesoporous microspheres constructed by the oriented organization of nanocrystals in sample 1 are much smaller (170 nm) than those of sample 6 (260 nm). These factors have effects on the BET-specific surface area, leading to the significant difference in BET-specific surface area between samples 1 and 6. These properties of α-Fe2O3 mesoporous microspheres will directly affect their photocatalytic activity, which will be discussed below.

Mentions:
We have measured the BET-specific surface areas and the pore size distributions of samples 1 and 6. Figure 5a, b shows the nitrogen adsorption–desorption isotherms and the pore size distributions of samples 1 and 6, which indicate that the BJH (Barrett–Joyner–Halenda) desorption average pore size and the BET-specific surface area are 4.3 nm and 114 m2/g for sample 1, and 7.9 nm and 37 m2/g for sample 6, respectively. Figure 5 indicates that there exist mesoporous structures in the α-Fe2O3 mesoporous microspheres. Sample 1 prepared at a lower temperature (120°C) has a much higher specific surface area and narrower pore size distribution than those of sample 6 prepared at a higher temperature (140°C). From the comparison of TEM micrographs of samples 1 and 6 (Figures 2, 4), one can see that the nanocrystals self-assembled in α-Fe2O3 mesoporous microspheres of sample 1 are smaller than those of sample 6. The oriented organization of smaller nanocrystals in α-Fe2O3 microspheres of sample 1 leads to smaller average pore size (4.3 nm); in contrast, the bigger nanocrystals in α-Fe2O3 microspheres of sample 6 result in larger average pore size (7.9 nm). On the other hand, the mesoporous microspheres constructed by the oriented organization of nanocrystals in sample 1 are much smaller (170 nm) than those of sample 6 (260 nm). These factors have effects on the BET-specific surface area, leading to the significant difference in BET-specific surface area between samples 1 and 6. These properties of α-Fe2O3 mesoporous microspheres will directly affect their photocatalytic activity, which will be discussed below.

Bottom Line:
In this approach, Fe(NO3)3 · 9H2O is used as the iron source, and polyvinylpyrrolidone (PVP) acts as a surfactant in the presence of NaCl in mixed solvents of H2O and ethanol.One of the advantages of this method is that the size of α-Fe2O3 mesoporous microspheres can be adjusted in the range from ca. 170 to ca. 260 nm by changing the experimental parameters.High photocatalytic activities in the degradation of salicylic acid are observed for α-Fe2O3 mesoporous microspheres with different specific surface areas.

ABSTRACTA simple one-step NaCl-assisted microwave-solvothermal method has been developed for the preparation of monodisperse α-Fe2O3 mesoporous microspheres. In this approach, Fe(NO3)3 · 9H2O is used as the iron source, and polyvinylpyrrolidone (PVP) acts as a surfactant in the presence of NaCl in mixed solvents of H2O and ethanol. Under the present experimental conditions, monodisperse α-Fe2O3 mesoporous microspheres can form via oriented attachment of α-Fe2O3 nanocrystals. One of the advantages of this method is that the size of α-Fe2O3 mesoporous microspheres can be adjusted in the range from ca. 170 to ca. 260 nm by changing the experimental parameters. High photocatalytic activities in the degradation of salicylic acid are observed for α-Fe2O3 mesoporous microspheres with different specific surface areas.